(Philadelphia, PA) - A protein with the ironic name “Srcasm”
can counteract the effects of tumor-promoting molecules in skin cells,
according to new research by investigators at the University of
Pennsylvania School of Medicine. Using animal models, the researchers
discovered that Srcasm acts like a brake in epithelial cells, preventing
uncontrolled cell growth caused by a family of proteins called Src kinases.
This finding, published online in the Journal of Biological Chemistry,
suggests a target for future gene therapy to treat skin, head, neck, colon,
and breast cancers.

Investigators have known for decades that Src kinase proteins can promote
tumor formation. Src kinase activity is elevated in most skin cancers
and in common carcinomas, including those of the breast and colon. At
the same time, levels of the signaling molecule Srcasm are typically low
in tumor cells, notes senior author John Seykora, MD,
PhD, Assistant Professor of Dermatology. The current findings
show that Srcasm can reduce the amount of Src kinases in cells; they have
also shown that increased activity of these kinases is associated with
cancerous skin lesions.

Src kinase proteins act like messengers, sending signals that control
cellular growth. Found just inside the cell membrane, they conduct signals
from cell surface receptors to the proteins that promote growth. Src kinases
can be activated during cell division or through mutation. If these proteins
are too active, they promote rapid cell growth that can spin out of control.
In skin cells, Src kinases and Srcasm are involved in signaling pathways
that control cell growth and differentiation.

See Saw Action
The researchers decided to test whether Srcasm could counteract the errant
effects of Src kinases. They developed strains of mice with high levels
of Srcasm, which had normal skin, and other strains that over-expressed
the Src-kinase called Fyn, which resulted in uncontrolled cell growth
with thick, scaly, hairless plaques on the skin. These plaques, or lesions,
resembled precursors of cancer. Breeding experiments with the mice indicated
that high Srcasm levels counteracted the effects of Fyn.

The findings reveal that levels of Fyn and Srcasm work in a kind of see-saw
- when Srcasm production is low, dangerous amounts of Fyn can build up
in cells. But when Srcasm production is increased, Fyn levels go down.
“The binding of Srcasm to Fyn regulates Fyn’s persistence
in the cell,” says Seykora. “If Srcasm is low, Fyn persists
longer and sends more growth-promoting signals.”

Reversing Tumors
Eventually, Srcasm might play a role in targeted gene therapies for cancers
that are triggered by activated Src kinases. Such a therapy would likely
use an adenovirus to carry a gene that codes for Srcasm into skin cells
to increase Srcasm production, as used in some other gene therapy treatments.
Initially, clinicians may try this method on oral cavity and skin cancers.

Next, the Penn researchers will determine whether Srcasm can actually
reverse tumor formation in skin. Seykora’s team has already prepared
an adenovirus and mice with the tumor-forming Src kinases expressed in
their skin. Within six months, the group expects to know whether Srcasm
can decrease squamous cell carcinoma formation in skin, mentions Seykora.

This research was funded by the National Institute of Arthritis and Musculoskeletal
and Skin Diseases. Other co-authors in addition to Seykora are Weijie
Li, Christine Marshall, Lijuan Mei, and Joel Gelfand, all from Penn.

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